INTERNAL FIELDS, DEFECTS, AND MOTIONS, STUDIED BY NUCLEAR METHODS.

Oriented radio-active nuclei, embedded in solids or liquids, can be used to obtain microscopic information on their environment. After production of the oriented probe nuclei interactions with surrounding fields cause their reorientation, which can be detected via a change of the anisotropy of the beta -or gamma -decay radiation. This has been applied to the study of internal magnetic fields, electric field gradients, internal motions, and phenomena connected with production and annealing of radiation defects. Illustrative experiments in insulators, semiconductors, and metals are presented.